Astrophysical Quantities of Cepheid Variables Measured with the Navy Prototype Optical Interferometer

Abstract

We present mean angular diameters for two cepheid variables, alpha Ursae\nMinoris and zeta Geminorum, determined with the Navy Prototype Optical\nInterferometer (NPOI). We present linear radii for these cepheids and two\nadditional cepheids, delta Cephei and eta Aquilae, previously observed at the\nNPOI. We find the limb-darkened angular diameter of alpha Ursae Minoris and of\nzeta Geminorum to be 3.28 +/- 0.02 and 1.55 +/- 0.09 milliarcseconds\nrespectively. Using trigonometric parallaxes, we find the linear radii of alpha\nUrsae Minoris, zeta Geminorum, delta Cephei and eta Aquilae to be 46 (+/- 3),\n60 (+25, -14), 45 (+8, -6), and 69 (+28, -15) Solar radii respectively. We\ncompare the pulsation periods and linear radii of this sample of cepheids,\nwhich range in period from three to 11 days, to theoretical and empirical\nperiod-radius and period-radius-mass relations found in the literature. We find\nthat the observed diameter of alpha Ursae Minoris is in excellent agreement\nwith the predicted diameter as determined from both surface brightness\ntechniques and theory only if alpha Ursae Minoris is a first overtone pulsator.\n